Thin film force sensors have been designed for a variety of purposes. Typically, such thin film sensors employ a pair of thin support sheets, one or more conductive ink electrodes on each support sheet with the conductive electrodes on the support sheets facing each other, pressure sensitive material between the facing electrodes, for example, in the form of a thin layer over each electrode, and an adhesive material bonding the sheets together.
Coverage over a wide area has been accomplished by using grids of electrodes. However, these require many, many terminals. In other cases, patterns of multiple electrode pairs have been used to provide coverage over a relatively wide area. Yet another possibility is to use very expansive electrode pairs, such as a pair of electrodes each three inches in diameter, or in another expansive configuration to cover a broad area, such as an area three inches in diameter. Although use of such large electrode pairs will reduce the number of terminals and leads necessary, large area electrodes are prone to spurious outputs and to the effects of shear forces. They also use substantial amounts of conductive ink, and, of course, substantial quantities of corresponding pressure sensitive resistive material.
Accordingly, a need arises for an improved wide-area pressure sensitive, thin-film sensing cell that is not prone to spurious outputs or to the effects of shear forces, that minimizes the use of inks, and that is effective, over the entire area, in producing a signal in response to a load that tends to be relatively broadly distributed, rather than occurring at only a point or a very small region.